Solution for use in extraction of cobalt, cobalt solution, and method for collecting cobalt

ABSTRACT

The purpose of the present invention is to provide a solution for use in the extraction of cobalt, whereby it becomes possible to extract cobalt at lower cost and more safely compared with a case in which a conventional one is used. The solution for use in the extraction of cobalt according to the present invention comprises: an ionic liquid containing a quaternary ammonium group; and an organic solvent which exists in such a state that the organic solvent is mixed with the ionic liquid and which has a kauri-butanol value of 60 or more.

TECHNICAL FIELD

This invention relates to a solution for use in extraction of cobalt, acobalt solution, and a method of collecting cobalt.

BACKGROUND ART

A cemented carbide alloy, which contains tungsten carbide as a maincomponent and cobalt, nickel, or the like as a binder metal and whichhas added thereto a carbide of titanium, tantalum, chromium, or the likefor improving performance, has been widely used in tools for metalprocessing or the like by virtue of its excellent hardness and abrasionresistance.

In the tools using such cemented carbide alloy, a tool which cannot beused any more due to a defect, abrasion, or the like during use or adefective part thereof is discarded as scrap called hard scrap.

Further, part of cemented carbide alloy powder generated duringmanufacturing of a cemented carbide tool, ground dust generated duringprocessing of the cemented carbide tool with a grinding stone, and thelike are discarded as scrap called soft scrap.

In the following description, the “cemented carbide scrap” refers toused scrap of an alloy containing 50 wt % or more of tungsten carbide,and cobalt or nickel as a binder phase.

The hard scrap and soft scrap each contain a large amount of tungsten,which is a rare metal. 60% or more of tungsten resources have been usedin the cemented carbide tools. Further, the prices of ammoniumparatungstate (APT) and tungsten oxide serving as intermediate rawmaterials for a tungsten material have continued to rise in recentyears, and there is a demand for establishment of a recycling technologyfor tungsten contained in the cemented carbide tools.

In view of the foregoing, a recycling method for a cemented carbide toolinvolving recycling tungsten carbide from a used cemented carbide toolor the like has been proposed, and specifically, a zinc method, a moltensalt dissolution method, an oxidizing roasting-alkali dissolutionmethod, or the like has been known (Patent Documents 1 and 2, and NonPatent Document 1).

Meanwhile, a residue produced at the time of the collection of tungstenby the method contains a large amount of cobalt, and hence thecollection of cobalt has also been desired. However, the residuecontains iron, manganese, nickel, copper, chromium, tantalum, tungsten,vanadium, or the like in addition to cobalt, and hence a problem interms of the purity of cobalt occurs when the residue is reused as acemented carbide raw material or when a cobalt base metal is producedfrom the residue.

Accordingly, there has been desired a technology involving separatingcobalt in the residue from which tungsten has been collected, followedby the purification and collection thereof.

A solvent extraction method (Cited Document 3) or a method of removing aprecipitate with a sulfide (Patent Document 4) has been reported as atechnology involving separating cobalt from iron and nickel.

However, the solvent extraction method has involved problems in terms ofsafety and cost because the method requires the use of a large amount ofa combustible hazardous solvent and requires an explosion-prooffacility. Meanwhile, the method of removing a precipitate with a sulfidehas involved problems in terms of an environmental load and themaintenance of a working environment because the method requires the useof a harmful sulfide.

In view of the foregoing, a method of extracting cobalt with an ionicliquid has been reported as a method of coping with those problems. Theterm “ionic liquid” as used herein means a liquid that: is a salt thatbecomes liquid at 100° C. or less; and is formed only of ions.

The ionic liquid has a structure formed of a cation portion and an anionportion. The extraction method involving using the ionic liquid isspecifically, for example, the following method (Non Patent Documents 2and 3). An ionic liquid containing a quatemary phosphonium group in thecation portion (hereinafter referred to as “quatemary phosphonium-basedionic liquid”) or an ionic liquid having a quatemary ammonium group inthe portion (hereinafter referred to as “quatemary ammonium-based ionicliquid) is used, and its viscosity is adjusted through mixing with anorganic solvent as required. After that, only cobalt is extracted in theionic liquid by bringing the ionic liquid, and a solution containingcobalt and nickel into contact with each other.

PRIOR ART DOCUMENTS Patent Document

-   Patent Document 1: JP-A-H11-505801-   Patent Document 2: WO 2010/104009 A1-   Patent Document 3: JP-A-2013-194269-   Patent Document 4: JP-A-2012-211375

Non Patent Document

-   Non Patent Document 1: Yasuhiko Tenmaya, Development Project for    Highly Efficient Recovery System for Rare Metal etc. “Recovery of    Tungsten etc. from Discarded Cemented Carbide Tools,” Mineral    Resources Report, Japan Oil, Gas and Metals National Corporation,    Vol. 38, No. 4, November, 2008, pp. 407-413-   Non Patent Document 2: Sil Wellens, Ben Thijs, Koen Binnemans. “An    environmentally friendlier approach to hydrometallurgy: highly    selective separation of cobalt from nickel by solvent extraction    with undiluted phosphonium ionic liquids” Green Chemistry, 2012, 14,    1657-   Non Patent Document 3: Patrycja Rybka et. al., Separation Science    and Technology, 47, 1296-1302, 2012

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, the technology described in Non Patent Document 2 or 3 hasinvolved such problems as described below.

First, the quatemary phosphonium-based ionic liquid is much moreexpensive than the quatemary ammonium-based ionic liquid, and hence thequatemary phosphonium-based ionic liquid has involved a problem in termsof cost when used for collecting cobalt from a used cemented carbidetool or the like.

In addition, the quatemary ammonium-based ionic liquid is less expensivethan the phosphonium-based ionic liquid, but has solubility in waterhigher than that of the quatemary phosphonium-based ionic liquid.

Accordingly, when the quatemary ammonium-based ionic liquid is used inthe extraction of cobalt from an aqueous solution containing cobalt, thefollowing problem occurs. The ionic liquid dissolves in the aqueoussolution and hence it becomes difficult to separate cobalt.

As described above, each of the related-art cobalt collectiontechnologies has involved a problem, and under the presentcircumstances, no technology that brings together low cost and highcollection efficiency has been available.

This invention has been made in view of the problems, and an object ofthis invention is to provide a solution for use in extraction of cobaltwith which cobalt can be extracted at lower cost and more efficientlythan ever before.

Means to Solve the Problem

To solve the problems, the inventors of this invention have madeinvestigations on the composition of an ionic liquid with which cobaltcan be extracted at lower cost and more efficiently than ever before,and which is less expensive than a phosphonium-based ionic liquid.

In particular, the inventors of this invention have made investigationson whether or not the solubility of a quatemary ammonium-based ionicliquid in water can be reduced.

As a result, the inventors have found that mingling the quatemaryammonium-based ionic liquid with a certain kind of organic solvent cansignificantly reduce the solubility in water, and hence enables theextraction of an ion from an aqueous solution containing cobalt. Thus,the inventors have completed this invention.

Specifically, a first aspect of this invention is a solution for use inextraction of cobalt comprising an ionic liquid containing a quatemaryammonium group and an organic solvent that is present in a state ofbeing mingled with the ionic liquid and has a kauri-butanol value of 60or more.

A second aspect of this invention is a cobalt solution comprising thesolution for use in extraction of cobalt of the first aspect and anaqueous solution of cobalt and an acid containing chlorine, the aqueoussolution being dissolved in the solution for use in extraction ofcobalt, wherein cobalt is dissolved in the solution for use inextraction of cobalt.

A third aspect of this invention is a method of collecting cobaltcomprising dissolving an aqueous solution of cobalt and an acidcontaining chlorine in a solution for use in extraction of cobalt, thesolution including an ionic liquid containing a quatemary ammoniumgroup, and an organic solvent that is present in a state of beingmingled with the ionic liquid and has a kauri-butanol value of 60 ormore, to dissolve cobalt in the solution for use in extraction of cobaltto separate and collect cobalt.

Effect of the Invention

According to this invention, the solution for use in extraction ofcobalt with which cobalt can be extracted at lower cost and moreefficiently than ever before can be provided.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart for illustrating an example of a cobaltextraction method of an embodiment of this invention.

FIG. 2 is a graph for showing a relationship between a mingling ratiobetween TOMAC (tri-octhyl-methyl-ammnoiumu-chloride) and an organicsolvent, and a viscosity.

FIG. 3 is a graph for showing a relationship between the mingling ratiobetween TOMAC and the organic solvent, and a Co extraction ability or aCo—Ni separation ability.

FIG. 4 is a flow chart of a cobalt extraction method of Examples.

MODE FOR EMBODYING THE INVENTION

A preferred embodiment of this invention is described in detail belowwith reference to the drawings.

Principle of This Embodiment

First, the principle of cobalt extraction of this embodiment is brieflydescribed.

In this embodiment, an ionic liquid is used for separating cobalt froman aqueous solution containing nickel and cobalt.

Specifically, first, an aqueous solution containing nickel, cobalt, andchlorine is prepared.

Specifically, a reaction represented by Equation 1 is caused bydissolving a compound containing nickel and cobalt in an acid containingchlorine, such as hydrochloric acid.

CoO+2HCl→CoCl₂+H₂O  Equation 1

A cobalt aqueous solution can be obtained because cobalt chloride to beproduced is water-soluble.

Next, the aqueous solution containing nickel, cobalt, and chlorine, andan ionic liquid having a chloride ion as an anion portion are broughtinto contact with each other.

At this time, cobalt in the aqueous solution is bonded to chlorine, andis extracted as a chloride complex into the ionic liquid.

Meanwhile, nickel does not form any chloride complex, and hence remainsin the aqueous solution and is separated from cobalt. The foregoing isthe principle of the cobalt extraction of this embodiment.

The reactions in which cobalt is thus extracted into the ionic liquidare shown below.

Co²⁺+4Cl⁻→CoCl₄ ²⁻  Equation 2

2I.L.-Cl+CoCl₄ ²⁻→(I.L.)₂-CoCl₄+Cl⁻(I.L.: cation portion of ionicliquid)   Equation 3

In addition, an extraction ability and a separation ability for cobaltare defined as follows.

Extraction ability: amount of cobalt (g/dm³=kg/m³) that can be extractedinto ionic liquid per unit volume

Separation ability: quotient (g/g) obtained by dividing amount of cobaltextracted into ionic liquid per unit volume by extraction amount ofnickel

Construction of This Embodiment

Next, the construction of a solution for use in extraction of cobalt tobe used in the cobalt extraction in this embodiment is described.

As described in the foregoing, the solution for use in extraction ofcobalt of this embodiment is configured to separate cobalt by beingbrought into contact with an aqueous solution containing cobalt andchlorine, and includes: an ionic liquid containing a quaternary ammoniumgroup; and an organic solvent that is present in a state of beingmingled with the ionic liquid and has a kauri-butanol value (hereinafterdescribed as “KB value”) of 60 or more.

The term “KB value” as used herein refers to the number of millilitersof a sample when a certain amount of a solution of a kauri resin inbutanol is loaded into an Erlenmeyer flask, the flask is placed onstandard printing type paper, the sample is added to the flask, and aprinting type becomes unreadable owing to the occurrence of turbidity.

(Ionic Liquid)

The ionic liquid is a liquid configured to extract cobalt by beingbrought into contact with an aqueous solution containing cobalt andchlorine, and in this embodiment, an ionic liquid containing a quatemaryammonium-based ionic liquid having a chloride ion as an anion portion isused.

This is because the quatemary ammonium-based ionic liquid is an ionicliquid much less expensive than other ionic liquids, such as a quatemaryphosphonium-based ionic liquid.

Examples of the quatemary ammonium-based ionic liquid include, but notnecessarily limited to, tri-octyl-methyl-ammonium-chloride(tri-octhyl-methyl-ammnoiumu-chloride, TOMAC) ordi-octadecyl-di-methyl-ammonium-chloride(di-octadethyl-di-methyl-ammoniumu-chloride).

(Organic Solvent)

The organic solvent of this embodiment is configured to reduce thesolubility of the ionic liquid containing a quatemary ammonium group inwater, and to adjust its physical properties, such as a viscosity, andan organic solvent having a KB value of 60 or more is used.

Now, the reason why the organic solvent having a KB value of 60 or moreis used is described.

As described above, a quatemary ammonium-based ionic liquid having achloride ion as an anion portion is an ionic liquid much less expensivethan other ionic liquids.

However, in an investigation on the extraction of a metal ion, aquatemary phosphonium-based ionic liquid much more expensive than thequatemary ammonium-based ionic liquid has been mainly used.

This is because the phosphonium-based ionic liquid does not dissolve inwater and has a low viscosity.

In contrast, the inexpensive ammonium-based ionic liquid involves aproblem in that the liquid mixes at a volume ratio of about 10% withwater, and a problem in that its viscosity is high. Particularly whencobalt is extracted, the viscosity becomes so high that the separabilityof the liquid from water becomes poor. Accordingly, the liquid cannot bepassed through, for example, a continuous extraction column.Accordingly, despite the fact that the ionic liquid having highextraction efficiency is used, a treatment can be performed only by abatch system poor in efficiency. The dissolution of the ionic liquid inwater leads to the discharge of the ionic liquid serving as an expensiveextractant to the outside of a system, and hence collection anddecomposition treatments for the ionic liquid need to be performed. Inaddition, the liquid involves a problem in that its ability to separatecobalt and nickel from each other is lower than that of thephosphonium-based ionic liquid.

To cope with the problems, the inventors of this invention havediscovered that the organic solvent having a KB value of 60 or moremingles with the quatemary ammonium-based ionic liquid, and in themingled state, the solubility of the liquid in water reduces and itsviscosity also reduces. Thus, the inventors have decided to use theorganic solvent having a KB value of 60 or more.

Examples of the organic solvent having a KB value of 60 or more includean alkylbenzene derivative and toluene. For example, when analkylbenzene derivative having a KB value of 80 (trade name: Solvesso150) is added at a volume ratio of about 10% to a quatemaryammonium-based ionic liquid, the viscosity of the solvent can be reducedto 1/10 or less. In addition, the separability of the quatemaryammonium-based ionic liquid from water is improved, and hence aphenomenon in which the liquid dissolves in water does not occur (thequatemary ammonium-based ionic liquid dissolves at a ratio of about 3%in terms of wt % in water before its mingling with the organic solvent,but the ratio is reduced to 0.01% or less after the mingling). Thus, theloss of the quatemary ammonium-based ionic liquid (dissolution in water)in an extraction treatment can be suppressed. An upper limit for the KBvalue is not particularly limited, but it is difficult to produce anorganic solvent that can be industrially utilized, the solvent having aKB value of more than 110.

A possible reason why mixing the organic solvent and the quatemaryammonium-based ionic liquid to mingle the solvent and the liquid witheach other can suppress the dissolution of the liquid in water is thatthe quatemary ammonium-based ionic liquid preferentially dissolves inthe hydrophobic organic solvent and hence its dissolution in water doesnot occur.

In addition, the quatemary ammonium-based ionic liquid dissolves inwater, and the water similarly dissolves in the quatemary ammonium-basedionic liquid. Nickel in the water cannot be separated by an extractiontreatment, and the ionic liquid needs to be washed after the extraction.However, when the quatemary ammonium-based ionic liquid is mixed withthe organic solvent to be mingled therewith, the amount of the waterdissolving in the quatemary ammonium-based ionic liquid reduces.Accordingly, the amount of nickel to be included also reduces, and hencethe ability of the solution for use in extraction of cobalt to separatecobalt and nickel from each other can be improved.

The foregoing is the description of the reason why the organic solventhaving a KB value of 60 or more is used.

The solution for use in extraction of cobalt desirably contains theorganic solvent at a volume ratio of 2% or more and 50% or less, andmore desirably contains the solvent at a volume ratio of 5% or more and15% or less. This is because of the following reasons: when the contentof the organic solvent is less than 2%, an effect of incorporating theorganic solvent is not obtained; and when the content is more than 50%,the Co extraction ability of the solution reduces because the organicsolvent is not involved in the extraction of Co.

In addition, the solution for use in extraction of cobalt desirablycontains the organic solvent so that its viscosity may be 0.02 Pa·s ormore and 0.5 Pa·s or less. This is because of the following reasons: alarge amount of the organic solvent needs to be incorporated forproducing a solution having a viscosity of less than 0.02 Pa·s, andhence the Co extraction ability reduces; and when the viscosity is morethan 0.5 Pa·s, it becomes difficult to perform a treatment with acontinuous extractor at the time of Co extraction. The viscosity of thesolution for use in extraction of cobalt reduces as the content of theorganic solvent therein increases. As described above, however, when thecontent is excessively large, the Co extraction ability reduces, andhence the content of the organic solvent needs to be set inconsideration of both the viscosity and the extraction ability.

<Cobalt Extraction Method>

Next, a cobalt extraction method involving using the solution for use inextraction of cobalt according to this embodiment is described withreference to FIG. 1.

The following method is given as an example herein. A cemented carbidescrap containing tungsten, cobalt, nickel, and iron is subjected tooxidizing roasting and an alkali extraction treatment or a molten saltdissolution treatment, and an aqueous solution of sodium tungstate thusproduced is filtered to produce a tungsten extraction residue, followedby the collection of a cobalt aqueous solution from the residue.

First, an acidic aqueous solution is prepared by bringing an acid, suchas hydrochloric acid or sulfuric acid, into contact with the tungstenextraction residue to leach out cobalt as cobalt chloride or cobaltsulfate into the aqueous solution (S1 of FIG. 1). The kind of the acidis preferably hydrochloric acid in consideration of a subsequenttreatment. However, when chlorine is supplied by using, for example,sodium chloride later, the kind of the acid is not necessarily limitedto hydrochloric acid as long as the acid is a strong acid, and sulfuricacid or the like is also permitted.

In addition, the concentration of the acid is desirably 1 N or more and10 N or less, more desirably 2 N or more and 5 N or less.

This is because of the following reasons: when the concentration of theacid is more than 10 N, the ratio at which manganese or copper isremoved at the time of an ion exchange treatment to be described laterreduces; and when the concentration of the acid is less than 1 N, acobalt concentration in a leachate (aqueous solution into which cobalthas been leached out) reduces to cause a reduction in treatmentefficiency or an increase in cost.

Next, hydrogen peroxide is added to the aqueous solution. The additionis intended for such oxidation of iron in the residue that iron may betrivalent. A specific addition amount thereof is about 0.5-fold mol ormore and about 3-fold mol or less of iron. When the addition amount is0.5-fold mol of iron, the amount is equal to that of iron and hence alliron can be oxidized.

The case where the addition amount of hydrogen peroxide is more than3-fold mol of iron is not desirable because excess hydrogen peroxidedecomposes to produce oxygen and oxygen is responsible for the entry ofair bubbles into a resin pipe at the time of the ion exchange to bedescribed later. Meanwhile, the case where the addition amount ofhydrogen peroxide is less than 0.5-fold mol of iron is not desirablebecause unoxidized iron remains in the solution. Iron is oxidizedimmediately after the hydrogen peroxide addition.

Next, iron is precipitated by adjusting the pH of the aqueous solutionto 1 or more and 6 or less with an alkali, such as sodium hydroxide orcalcium hydroxide, and the precipitated iron is removed by filtration orthe like (S2 of FIG. 1).

A specific alkali is preferably a hydroxide formed of a monovalentcation, and is preferably sodium hydroxide in consideration of cost.This is because of the following reason: when the finally extracted Cois used as a raw material for a cemented carbide tool, Co needs to beprecipitated by adding oxalic acid to the Co aqueous solution, but whena hydroxide formed of a divalent cation is used in the S2, the hydroxideis precipitated together with cobalt at the time of the production ofthe oxalic acid precipitate, and is liable to be included as animpurity. However, when Co is directly reduced, there is no need tolimit the alkali to the hydroxide formed of a monovalent cation, andcalcium hydroxide, magnesium hydroxide, potassium hydroxide, strontiumhydroxide, cobalt hydroxide, or the like can be used. However, acarbonate, such as sodium carbonate, is not desirable because cobaltcarbonate is produced, and ammonia is not desirable because acobalt-ammine complex is produced and hence cobalt cannot be extractedinto an ionic liquid.

The precipitated iron is removed by filtration. In addition, the casewhere the pH is more than 6 is not desirable because cobalt isprecipitated as a hydroxide and hence the ratio at which cobalt iscollected reduces. In addition, the case where the pH is less than 1 isnot desirable because the precipitation of iron does not completelyprogress, and hence the ratio at which iron is removed reduces, and theratios at which manganese and copper are removed by the subsequent ionexchange also reduce.

Next, a chloride is added to the aqueous solution to set its chlorideion concentration to 2-fold mol or more of cobalt. The addition isintended for efficient extraction of cobalt into the ionic liquid.

When hydrochloric acid is used in the cobalt leaching treatment(treatment corresponding to the S1 of FIG. 1), the addition of thechloride here is not essential.

Next, manganese and copper are removed by bringing the aqueous solutioninto contact with an ion exchange resin (S3 of FIG. 1).

Specifically, it is desirable that a chelate-type anion exchange resinhaving a volume equal to or more than 1/100 of the volume of the aqueoussolution be immersed in the aqueous solution for 10 minutes or more, orthe aqueous solution be passed after the ion exchange resin has beenfilled into a column.

The case where the volume of the resin is less than 1/100 of the volumeof the aqueous solution is not desirable because the ratios at whichmanganese and copper are removed reduce.

In addition, the case where the time period for which the resin isimmersed is less than 10 minutes is not desirable because the ratios atwhich manganese and copper are removed reduce.

In addition, when the aqueous solution is passed after the filling intothe column, the solution is passed at a space velocity (SV) of 0.1 ormore and 10 or less.

The case where the space velocity at the time of the filling into thecolumn is less than 0.1 is not desirable because the removal treatmenttakes time and such time-consuming treatment is not realistic.

In addition, the case where the space velocity at the time of thefilling into the column is more than 10 is not desirable because thebreakthrough of manganese and copper quickens, and hence the frequencyat which the ion exchange resin is reproduced increases.

Next, the ionic liquid mingled with an organic solvent in advance isbrought into contact with the aqueous solution so that Co may beextracted and dissolved in the ionic liquid, and may be separated fromnickel (S4 of FIG. 1). A method for the contact may be a batch-typemethod or may be a continuous method as in a general solvent extractiontreatment. Nickel remains in the aqueous solution and is hencecollected.

In addition, a chlorine concentration at the time of the contact betweenthe ionic liquid and the aqueous solution is desirably 2-fold molarconcentration or more and 10-fold molar concentration or less of thecobalt concentration.

This is because of the following reason: when the chlorine concentrationis more than 10-fold molar concentration of the cobalt concentration,the concentration becomes close to the upper limit at which a generalchloride, such as sodium chloride or calcium chloride, dissolves inwater, and hence the dissolution takes much time, and when theconcentration is further increased, a precipitate remains, and hence itbecomes difficult to separate the quaternary ammonium-based ionic liquidand the precipitate from each other.

This is also because when the chlorine concentration is less than 2-foldmolar concentration of the cobalt concentration, a chloride complex ofcobalt is hardly produced and hence an extraction ability reduces.

Finally, the solution into which cobalt has been extracted (hereinafterreferred to as “cobalt solution”) is brought into contact with water,such as pure water (S5 of FIG. 1).

The pure water is free of any chloride ion, and hence the chloridecomplex of cobalt decomposes and cobalt is subjected to back extractioninto the pure water. As the temperature of the pure water becomes lower,cobalt can be extracted more efficiently.

The foregoing is the cobalt extraction method of this embodiment.

As described above, the solution for use in extraction of cobalt of thisembodiment includes: an ionic liquid containing a quaternary ammoniumgroup; and an organic solvent that is present in a state of beingmingled with the ionic liquid and has a kauri-butanol value of 60 ormore.

Accordingly, cobalt can be extracted at lower cost and more efficientlythan ever before.

EXAMPLES

This invention is specifically described below with reference toExamples.

Example 1

A quatemary ammonium-based ionic liquid was brought into contact withvarious organic solvents, whether or not the liquid was able to minglewith each of the solvents was judged, and as a change in physicalproperty when the liquid was able to mingle with a solvent, theviscosity of a solution obtained by the mingling was measured.

Specifically, first, TOMAC was prepared as the quatemary ammonium-basedionic liquid.

Next, organic solvents each having a KB value of from 30 to 100 wereprepared as the organic solvents, and TOMAC and each of the organicsolvents were brought into contact with each other. A relationshipbetween a used organic solvent and its KB value is as described below.

Organic solvent having KB value of 30: Isopar C (isoparaffin-basedsolvent manufactured by Exxon Mobil Corporation), organic solvent havingKB value of 40: Exxsol DSP 80 (naphthene-based solvent manufactured byExxon Mobil Corporation), organic solvent having KB value of 60:cyclohexane, organic solvent having KB value of 80: Solvesso 150(aromatic solvent manufactured by Exxon Mobil Corporation), and organicsolvent having KB value of 100: toluene. The results are shown in Table1.

TABLE 1 KB value 30 40 60 80 100 Whether or not Impossible ImpossiblePossible Possible Possible quaternary ammonium-based ionic liquid canmingle with organic solvent

As apparent from Table 1, an organic solvent having a KB value of lessthan 60 did not mingle with TOMAC, and the solvent and TOMAC wereseparated into two phases. Meanwhile, a solvent having a KB value of 60or more was confirmed to mingle with TOMAC.

Next, Solvesso 150 was prepared as a solvent having a KB value of 60 ormore out of the organic solvents. The Solvesso 150 was mingled atvarious ratios with TOMAC, and an influence of a mingling ratio on theviscosity of a solution obtained by the mingling was measured. Theresults are shown in FIG. 2.

As shown in FIG. 2, it was able to be confirmed that when the minglingratio of the organic solvent was increased, the viscosity of thesolution obtained by the mingling reduced in a substantially linearmanner. Accordingly, the addition of the organic solvent to TOMAC wasfound to affect its physical properties.

Example 2

A solution (solution for use in extraction of cobalt) in which aquatemary ammonium-based ionic liquid and an organic solvent mingledwith each other was brought into contact with an aqueous solution of Coand Ni, and was evaluated for its extraction ability and separationability for Co. Specific procedures are as described below.

First, TOMAC was prepared as the quatemary ammonium-based ionic liquidand Solvesso 150 was prepared as the organic solvent. The solution foruse in extraction of cobalt was produced by mingling TOMAC and theorganic solvent with each other at a mingling ratio of from 0 vol % to60 vol %.

Next, the aqueous solution of Co and Ni (Co: 43 g/dm³, Ni: 1.0 g/dm³)was produced by dissolving Co and Ni in a 4 mol/L hydrochloric acid. Theunit “g/dm³” is equal to the unit “kg/m³” (the same holds true for thefollowing).

Next, the aqueous solution of Co and Ni, and the solution for use inextraction of cobalt were loaded into a separating funnel, and werebrought into contact with each other by shaking the funnel for 10minutes so that Co was caused to migrate toward the solution for use inextraction of cobalt. Thus, Co was extracted and Ni was caused to remainin the aqueous solution.

Next, the Co and Ni concentrations of the aqueous solution before andafter the extraction were determined and analyzed by ICP-AES, and a Coextraction ability and a Co—Ni separation ability were calculated from adifference between the concentrations of each element before and afterthe extraction. The results are shown in FIG. 3.

As shown in FIG. 3, as the volume ratio of the Solvesso 150 increased,the Co extraction ability reduced. This is probably because the Solvesso150 in the solvent is not involved in the extraction of Co.

Meanwhile, as the volume ratio of the Solvesso 150 increased, the Co—Niseparation ability was improved. This is probably because as the ratioof the Solvesso 150 increased, the hydrophobicity of the solution foruse in extraction of cobalt was improved and hence the dissolution ofthe aqueous solution containing Ni in the solution for use in extractionof cobalt was suppressed.

Example 3

An attempt was made to extract Co from a compound (cobalt residue)containing cobalt, copper, chromium, manganese, iron, and nickel by theCo extraction method according to this embodiment in accordance withprocedures illustrated in FIG. 4. Specific procedures are as describedbelow.

First, an acid leachate was obtained by dissolving 130 g of the cobaltresidue in 1,000 ml of hydrochloric acid (concentration: 2 mol/l) as anacid (S11 of Fig.). The concentrations (mg/dm³) of the metal componentsin the acid leachate are as follows: Cu: 1, Cr 150, Mn: 27, Fe: 1,460,Ni: 500.

Next, iron was precipitated by adding 2 ml of a hydrogen peroxidesolution (concentration: 0.59 mol/l) and sodium hydroxide(concentration: 8 mol/l) to the acid leachate to set its pH to 3,followed by the collection of iron (S12 of Fig.).

Next, Mn and Cu were removed from the acid leachate from which iron hadbeen removed by bringing the acid leachate into contact with an ionexchange resin (50 ml) to cause the ion exchange resin to adsorb Mn andCu (S13 of Fig.).

Next, the acid leachate from which Mn and Cu had been removed wasbrought into contact with a solution for use in extraction of cobaltobtained by mingling TOMAC serving as an ionic liquid and Solvesso 150serving as an organic solvent with each other (mingling ratio: 10:1).Thus, cobalt was extracted into the ionic liquid in the solution for usein extraction of cobalt (S14 of Fig.).

Finally, cobalt was subjected to back extraction into pure water bybringing the solution for use in extraction of cobalt into contact withthe pure water (S15 of Fig.).

The results of the quantitative analysis of the metal concentrations inthe aqueous solution in the respective procedures by ICP-AES are shownin Table 2.

TABLE 2 After precipi- After acid tation After ion After After backTreatment leaching treatment exchange extraction extraction stage (afterS11) (after S12) (after S13) (after S14) (after S15) Cu mg/dm³ 1 1 <1 <1<1 Cr mg/dm³ 150 8 3 <1 1 Mn mg/dm³ 27 9 2 <1 3 Fe mg/dm³ 1,460 <2 <2 <2<2 Ni mg/dm³ 500 490 280 89 <2

As apparent from Table 2, the metals were sequentially removed in therespective procedures, and Co was finally purified.

INDUSTRIAL APPLICABILITY

While this invention has been described above with reference to theembodiment and Examples, this invention is not limited to theabove-mentioned embodiment.

It should be understood that a person skilled in the art could arrive atvarious modification examples and improvement examples within the scopeof this invention, and that those modification examples and improvementexamples are encompassed in the scope of this invention.

1. A solution for use in extraction of cobalt, comprising: an ionicliquid containing a quaternary ammonium group; and an organic solventthat is present in a state of being mingled with the ionic liquid andhas a kauri-butanol value of 60 or more.
 2. A solution for use inextraction of cobalt according to claim 1, wherein the solutioncomprises the organic solvent at a volume ratio of 2% or more and 50% orless.
 3. A solution for use in extraction of cobalt according to claim1, wherein the solution comprises the organic solvent at a volume ratioof 5% or more and 15% or less.
 4. A solution for use in extraction ofcobalt according to claim 1, wherein the organic solvent comprises analkylbenzene derivative or toluene.
 5. A solution for use in extractionof cobalt according to claim 1, wherein the ionic liquid comprisestri-octyl-methyl-ammonium-chloride (TOMAC) ordi-octadecyl-di-methyl-ammonium-chloride.
 6. A solution for use inextraction of cobalt according to claim 1, wherein the solution has aviscosity of 0.02 Pa·s or more and 0.5 Pa·s or less.
 7. A solution foruse in extraction of cobalt according to claim 1, wherein the solutionhas a solubility in water of 0.01% or less.
 8. A cobalt solution,comprising: the solution for use in extraction of cobalt of claim 1; andan aqueous solution of cobalt and an acid containing chlorine, theaqueous solution being dissolved in the solution for use in extractionof cobalt, wherein cobalt is dissolved in the solution for use inextraction of cobalt.
 9. A method of collecting cobalt, comprisingdissolving an aqueous solution of cobalt and an acid containing chlorinein a solution for use in extraction of cobalt, the solution including anionic liquid containing a quaternary ammonium group, and an organicsolvent that is present in a state of being mingled with the ionicliquid and has a kauri-butanol value of 60 or more, to dissolve cobaltin the solution for use in extraction of cobalt to separate and collectcobalt.
 10. A method of collecting cobalt according to claim 9, whereinthe method comprises: (a) dissolving a compound containing cobalt in anacid to prepare an acidic aqueous solution; (b) dissolving the acid inthe solution for use in extraction of cobalt to extract cobalt into thesolution for use in extraction of cobalt; and (c) bringing the solutionfor use in extraction of cobalt into contact with water to perform backextraction of cobalt into the water, followed by collection thereof. 11.A method of collecting cobalt according to claim 9, wherein the solutionfor use in extraction of cobalt contains the organic solvent at a volumeratio of 2% or more and 50% or less.
 12. A method of collecting cobaltaccording to claim 9, wherein the solution for use in extraction ofcobalt contains the organic solvent at a volume ratio of 5% or more and15% or less.
 13. A method of collecting cobalt according to claim 9,wherein the organic solvent comprises an alkylbenzene derivative ortoluene.
 14. A method of collecting cobalt according to any claim 9,wherein the ionic liquid comprises tri-octyl-methyl-ammonium-chloride(TOMAC) or di-octadecyl-di-methyl-ammonium-chloride.
 15. A method ofcollecting cobalt according to claim 10, wherein: the compound containsnickel; and the (b) comprises dissolving the acidic aqueous solution inthe solution for use in extraction of cobalt to extract cobalt into thesolution for use in extraction of cobalt, and to collect nickelremaining in the acidic aqueous solution.
 16. A method of collectingcobalt according to claim 10, wherein: the compound contains at leastone of manganese and copper; and the method further comprises (d)bringing the acidic aqueous solution into contact with a chelate resinto separate at least one of manganese and copper from the acidic aqueoussolution.
 17. A method of collecting cobalt according to claim 10,wherein: the compound contains iron; and the method further comprises(e) removing iron from the acidic aqueous solution.
 18. A method ofcollecting cobalt according to claim 17, wherein the (e) comprises:adding hydrogen peroxide to the acidic aqueous solution to oxidize iron;adjusting a pH of the acidic aqueous solution to 1 or more and 6 or lessto precipitate iron; and removing the precipitated iron by filtration.19. A method of collecting cobalt according to claim 10, wherein the (a)comprises adding a chloride to the acidic aqueous solution.
 20. A methodof collecting cobalt according to claim 10, wherein the compoundcontains a residue after collection of tungsten from a cemented carbidescrap containing tungsten and cobalt.